1. Field of the Invention
The present invention relates to a photosensitive paste composition and a plasma display panel (PDP) manufactured using the same. More particularly, the present invention relates to a photosensitive paste composition for forming a black layer on top of barrier ribs preventing electrical or optical crosstalk between adjacent discharge cells to achieve better contrast, and a PDP manufactured using the same.
2. Description of the Related Art
In a conventional a plasma display panel (PDP), a barrier rib is a structure formed on a rear panel (or a rear substrate), and serves to define a discharge space and to prevent electrical or optical crosstalk between adjacent discharge cells. The barrier rib is formed on a dielectric layer covering address electrodes by screen printing, sandblasting, photolithography, or the like.
In the case of forming a barrier rib using screen printing, a barrier rib paste for printing is printed on a substrate using a patterned mask and a squeeze and dried to remove a solvent. The printing and drying are repeated several times to obtain a film with a desired thickness. The obtained film is sintered to thereby form a barrier rib. However, this method is time-consuming, and has difficulty in forming a uniformly patterned barrier rib due to misalignment by low resolution and repeated printing.
In the case of forming a barrier rib using sandblasting, a barrier rib paste is once printed on a substrate by a table coater and dried to obtain a film with a desired thickness. A dry film resist with sanding resistance is then laminated on the film and patterned through exposure to light and development. Then, micro-abrasive sandblasting is performed under a high pressure using the dry film resist pattern as a mask to obtain a patterned film. A residual dry film resist is removed, and the patterned film is sintered to complete a barrier rib. Although a barrier rib formed by sandblasting has higher resolution than that formed by screen printing, the sandblasting method has disadvantages such as complicated process and damage to electrode terminals due to collision of them with abrasive agents.
In the case of forming a barrier rib using photolithography, a photosensitive paste is printed and dried to form a film with a desired thickness. The film is exposed to UV light by a UV exposure system equipped with a photomask. The printing, drying, and exposure are repeated several times. Developing is then performed to selectively remove an unexposed region, followed by sintering, to obtain a barrier rib. Photolithography can form a barrier rib with higher resolution relative to screen printing and does not require a dry film resist and a sanding process unlike a sandblasting method. However, there are disadvantages such as many processes and misalignment due to repeated processes.
In view of the above problems, U.S. Pat. No. 6,197,480 entitled Photosensitive paste, a plasma display, and a method for the production thereof to Iguchi, et al. discloses a method of forming a barrier rib by minimizing a difference in refractive index between an inorganic material and an organic material. Korean Patent Laid-Open Publication No. 2004-12298 discloses a surface treatment of an inorganic material with fumed silica. The surface treatment with the fumed silica enables enhancement of exposure sensitivity, which enables the formation of a barrier rib through a single exposure process.
However, barrier ribs formed by these methods consist of a single white layer. Thus, visible light emitted from phosphor layers disposed in spaces defined by the barrier ribs is reflected by the barrier ribs, thereby enhancing brightness. However, the barrier ribs also reflect incident light from a front panel, thereby lowering image contrast.
Furthermore, a recent trend in a photosensitive paste used in forming a barrier rib by photolithography is the increasing use of water or an aqueous alkaline solution as a developer instead of an organic solvent considering environmental problems. In this regard, a copolymer containing an acidic functional group such as a carboxyl group is used as an organic binder which is a paste component. However, the carboxyl group-containing copolymer used as the organic binder is ionically cross-linked with inorganic powders which are a major paste component to facilitate the formation of a three-dimensional network structure (gelation). Such gelation rapidly increases the viscosity of a paste, which makes printing or developing impossible.
Several approaches for preventing the gelation of a paste have been suggested. For example, U.S. Pat. No. 6,576,391 entitled Photosensitive paste, a plasma display, and a method for the production thereof to Iguchi, et al. discloses a surface treatment of inorganic powders with a triazole compound, and U.S. Pat. No. 6,326,125 entitled Photosensitive composition and calcined pattern obtained by use thereof to Kakimura, et al. discloses a use of a sterically hindering copolymer. Although these methods can retard the gelation of a paste, the gelation cannot be fundamentally prevented.